The SLiDE experiment is designed to study surface tension driven flows in fusion relevant magnetic fields and conditions. With the conclusion of the liquid lithium helium retention experiments at UIUC, a new experiment is being planned to study new effects which may impact divertor and limiter designs of future fusion devices. The CDX-U experiment at PPPL showed remarkable power-handling capabilities when spot heated by an electron beam. The lithium is capable of advecting heat deposited locally throughout the rest of the tray due to surface tension effects, sometimes called, “Marangoni Flow”. The SLiDE experiment is being designed to study the surface tension effects in the presence of an externally applied magnetic field.
Surface tension is a monotonically decreasing function with temperature. At the free surface of a lithium pool, a temperature gradient produces a surface-tension gradient which in turn, induces a flow. In the presence of a magnetic field, a conductor moving perpendicular to the field experiences a drag due to the Lorentz force. This can radically alter liquid metal flows. With local heating or other surface tension effects, the magnitude of the liquid flow will balance between surface tension driven forces and MHD drag. The velocity depends upon the magnetic field strength and the size of the temperature gradient along the surface.
The liquid lithium flow will be diagnosed using local heat flux measurements through out a static tray containing the lithium pool. An electron beam line-source will be used to create a 2-dimensional geometry for the flow. This, however, may be complicated by thermoelectric effects arising from the temperature gradients at the interface between the tray and the pool. Exploitation of both the thermoelectric effect and surface tension effects may allow novel designs for liquid lithium plasma facing components to be made. The SLiDE experiment will explore the interaction between these effects.
A specially designed electron beam heat source has been implemented and is currently operation for the SLiDE apparatus. At full power (15kW), the beam is capable of subjecting a target material with a peak heat flux of 36 MW/m^2. On average, the mean power flux through the tray system is nearly 2MW/m^2 which is the expected first-wall loading in fusion reactor designs. The beam has been characterized during operation over a range of applied magnetic fields to provide an accurate assessment of the current density profile for all cases examined.
As of May, 2009, the SLiDE Facility is fully operational. The current testing schedule involves the examination of bulk pools of liquid lithium under the electron beam heat flux. Future testing can include other liquid metals and even non-liquid plasma facing component materials which require fusion-relevant heat flux exposure.